He was clear, however, on where the greatest threat to the United States now lies, accusing Democratic frontrunner Hillary Clinton of a refusal to name it.

"Containing the spread of radical Islam must be a major foreign policy goal of the United States and, indeed, the world," he said.

David Pollock, a former senior State Department advisor and now Washington Institute fellow, said the speech would help Trump with Washington experts.

"It seemed to be a more appealing presentation and Trump themes in a softer and smarter way, but left many questions unanswered," he told AFP. "So people are probably kind of taking a sceptical stance but then see what he follows up with," he said.

"And a key test of that will be what kind of new advisors he can find who will publicly side with him and join the team."

Trump has been widely mocked for failing to secure big-name foreign policy endorsements and relying on a coterie of right-wing fringe figures.

But he defended his team, slamming the available talent in Washington circles as tainted by the chaos unleashed under President George W Bush.

"My goal is to establish a foreign policy that will endure for several generations," he said.

"That's why I also look and have to look for talented experts with approaches and practical ideas rather than surrounding myself with those who have perfect resumes but very little to brag about except responsibility for a long history of failed policies and continued losses at war."

But many experts noted that Trump was announced at the podium by one of Bush's closest advisors on the Middle East, former ambassador Zalmay Khalilzad.

This, observers said, was a sign that as Trump's nomination appears more and more likely, more leading Republicans would come to his side.

Michael Pregent, former intelligence advisor to Iraq war commander general David Petraeus and a fellow of the Hudson Institute, called the speech "disjointed".

"He said to our allies 'we'll be there to help you' but then he says earlier in the speech that they'll have to pay for themselves and do more," he said.

This view was echoed by former Virgina governor and former Trump rival for the Republican ticket Jim Gilmore, who attended the speech.

"There was a lot in the talk that I would absolutely agree with," he admitted.

"On the other hand there is a lot in this speech that contradicts that, that talks about pulling back, confronting if you will our allies much more."

The Straits Times

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